asp.net-mvc 从 Razor View 接收 POST 请求时，为什么我得到 null 而不是空字符串？
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Why do I get null instead of empty string when receiving POST request in from Razor View?
提问by Alex
I used to receive empty string when there was no value:
我曾经在没有值时收到空字符串：
[HttpPost]
public ActionResult Add(string text)
{
// text is "" when there's no value provided by user
}
But now I'm passing a model
但现在我正在传递一个模型
[HttpPost]
public ActionResult Add(SomeModel Model)
{
// model.Text is null when there's no value provided by user
}
So I have to use the ?? ""operator.
所以我必须使用?? ""运算符。
Why is this happening?
为什么会这样？
回答by Michael Jubb
You can use the DisplayFormatattribute on the property of your model class:
您可以DisplayFormat在模型类的属性上使用该属性：
[DisplayFormat(ConvertEmptyStringToNull = false)]
回答by hackerhasid
The default model binding will create a new SomeModel for you. The default value for the string type is null since it's a reference type, so it's being set to null.
默认模型绑定将为您创建一个新的 SomeModel。字符串类型的默认值是 null，因为它是一个引用类型，所以它被设置为 null。
Is this a use case for the string.IsNullOrEmpty() method?
这是 string.IsNullOrEmpty() 方法的用例吗？
回答by user2284063
I am trying this in Create and Edit (my object is called 'entity'):-
我正在创建和编辑中尝试此操作（我的对象称为“实体”）：-
if (ModelState.IsValid)
{
RemoveStringNull(entity);
db.Entity.Add(entity);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(entity);
}
Which calls this:-
这称为：-
private void RemoveStringNull(object entity)
{
Type type = entity.GetType();
FieldInfo[] fieldInfos = type.GetFields(BindingFlags.Instance | BindingFlags.GetField | BindingFlags.Public | BindingFlags.NonPublic);
for (int j = 0; j < fieldInfos.Length; j++)
{
FieldInfo propertyInfo = fieldInfos[j];
if (propertyInfo.FieldType.Name == "String" )
{
object obj = propertyInfo.GetValue(entity);
if(obj==null)
propertyInfo.SetValue(entity, "");
}
}
}
It will be useful if you use Database First and your Model attributes get wiped out each time, or other solutions fail.
如果您使用数据库优先并且您的模型属性每次都被清除，或者其他解决方案失败，这将非常有用。
